Materials Processing Using Highly Concentrated Solar Radiation

Highly concentrated radiant energy provides a controllable means of delivering large flux densities (>100 W/cm/sup 2/) to solid surfaces. The resulting thermal energy can cause phase changes, atomic migrations, and chemical reactions on a surface without greatly perturbing the bulk properties, or the photons may directly interact with species on the surface to induce some desirable interaction. In a suitably designed solar furnace this flux can be delivered over large areas or tailored to accommodate particular processing requirements. Furthermore, this occurs without the environmental liability associated with providing power to more conventional light sources. Research to date has demonstrated the possibility of performing several interesting surface modifications, including phase transformation hardening of stools, melting powders or preapplied coatings to form fully dense, well-bonded coatings, initiation of self-propagating high-temperature synthesis reactions, rapid thermal annealing, and chemical vapor deposition. Particularly interestin results have been obtained in the cladding work, and the results of efforts to control the physical properties of the interfacial regions of coatings on steel is discussed in some detail.